1. Field of the Invention
The present invention generally relates to an electronic ballast system for emergency lighting applications, and more particularly, to a compact single-stage electronic ballast circuit. The system integrates the features of battery charger/discharger and lamp ballast so as to reduce the fabrication cost and the number of switching elements.
2. Description of the Prior Art
To comply with regulation and safety requirements, emergency lighting equipment becomes indispensable. In the prior art of emergency lighting technique, researchers have presented several viable approaches to emergency lighting applications. There is, however, a common drawback of requiring a complicated converter topology, which might result in the high cost and increasing number of switching elements. Accordingly, a single-stage system integrating plural power converters to reduce the fabrication cost has become a future research tendency.
Please refer to FIG. 1A, which is a commonly used circuit configuration for bi-direction flyback converter serving as either a charger or a discharger. FIG. 1B shows the normal configuration of a half-bridge series-resonant parallel-loaded inverter (SRPLI), in which Vc1=Vc2. For a practical emergency lighting application, the battery voltage VB in FIG. 1A is usually much lower than the rectified line voltage Vdc. Thus, to combine the bi-directional flyback converter with SRPLIs, it requires an additional transformer to boost up the battery voltage. The inverter of FIG. 1B also serves as an electronic ballast for lighting. A multi-stage power converter shown as FIG. 2 consists of a regular/emergency ballast 200 including S1 and S2, a bi-directional flyback converter 220 including S3 and S4 and a regular ballast 240 including S5 and S6. FIG. 2 shows the original inverter/charger/discharger converter that has not been modified. This invention will incorporate the multi-stage inverter/charger/discharger converter into a single-stage converter.
Applications of a multi-stage power converter shown in FIG. 2 are undermined due to the requirement of the increased number of switching elements. Such a multi-stage power converter employs a considerable amount of elements, which results in high fabrication cost. Furthermore, the overall power conversion efficiency may also decrease due to the multi-stage conversion. These drawbacks are unacceptable since the modern-day standards require the high efficiency and low cost. Therefore, efforts have been made to provide single-stage converters with multiple functions so as to overcome the foregoing problems.